U.S. patent number 4,662,269 [Application Number 06/730,836] was granted by the patent office on 1987-05-05 for selective zone isolation for hvac system.
Invention is credited to Jerry J. Tartaglino.
United States Patent |
4,662,269 |
Tartaglino |
* May 5, 1987 |
Selective zone isolation for HVAC system
Abstract
An activity zone of a house is selectively isolated with respect
to a sleeping zone during nighttime intervals by selectively
blocking the flow of conditioned air into the activity zone, while
allowing the usual flow of conditioned air into the sleeping zone.
The air flow passage in each supply duct is blocked by an
inflatable air bladder disposed within the air flow passage. An air
compressor is coupled to the bladder for inflating it to cause it
to expand against the sidewall of the duct and seal the air flow
passage during the isolation mode of operation, and for drawing air
from the bladder to cause it to collapse and open the air flow
passage during the conditioned air supply mode of operation. In the
preferred embodiment, operation of the compressor is coordinated by
a timer and a solenoid controlled, four-way valve which ports
pressurized air to the bladders during a preprogramed zone
isolation interval, and directs the withdrawal of air from the
bladders during a preprogramed conditioned air supply interval. A
pressure responsive power switch applies operating power to the
compressor in response to compressor discharge port pressure being
less than the pressure level corresponding with a fully inflated
air bladder, and removes operating power from the compressor in
response to the compressor inlet port pressure being less than the
pressure level corresponding with the air bladder being in the
collapsed condition.
Inventors: |
Tartaglino; Jerry J. (Dallas,
TX) |
[*] Notice: |
The portion of the term of this patent
subsequent to June 11, 2002 has been disclaimed. |
Family
ID: |
27080281 |
Appl.
No.: |
06/730,836 |
Filed: |
May 6, 1985 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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588443 |
Mar 12, 1984 |
4522116 |
|
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Current U.S.
Class: |
454/255;
251/61.1; 236/46R; 454/333 |
Current CPC
Class: |
F24F
3/044 (20130101); F24F 13/0236 (20130101); F24F
7/06 (20130101); F24F 11/0001 (20130101); F24F
2013/087 (20130101); Y02B 30/70 (20130101); Y02B
30/767 (20130101) |
Current International
Class: |
F24F
3/044 (20060101); F24F 11/00 (20060101); F24F
7/06 (20060101); F24F 011/00 () |
Field of
Search: |
;98/39.1,41.1 ;165/12
;236/46R,49 ;417/19,44 ;251/61.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Joyce; Harold
Attorney, Agent or Firm: Glaser, Griggs & Schwartz
Parent Case Text
This is a continuation of application Ser. No. 06/588,443, filed
Mar. 12, 1984 now U.S. Pat. No. 4,522,116.
Claims
What is claimed is:
1. Apparatus for opening and closing an air flow duct of the type
having a tubular sidewall surrounding an air flow passage, said
apparatus comprising, in combination:
an inflatable air bladder for insertion into the air flow passage,
said bladder being adapted to expand against the sidewall of said
duct when pressurized and to retract from the sidewall and assume a
minimum profile, collapsed condition when evacuated to a pressure
less than ambient atmospheric pressure;
pumping means coupled to said bladder for inflating said bladder
with pressurized air to cause it to expand against the sidewall and
seal the air flow passage during an isolation interval, and for
pumping air out of said bladder until its interior pressure is less
than ambient atmospheric pressure to cause it to collapse to the
minimum profile condition and open the air flow passage during a
supply interval; and,
power switching means coupled to said pumping means enabling
operation of said pumping means in response to the interior air
pressure of said air bladder being less than a first pressure level
corresponding with the inflation pressure of said bladder when it
is in the expanded, duct sidewall engaging condition, and for
inhibiting operation of said pumping means (a) in response to the
inflation pressure of said bladder being greater than said first
pressure level, or (b) in response to the collapsed pressure of
said bladder being less than a second pressure level below ambient
atmospheric pressure corresponding with the vacuum pressure of said
bladder when it is in the evacuated, minimum profile condition.
2. An energy management system for use in combination with an air
supply duct having air flow passage comprising, in combination:
an inflatable air bladder for insertion into the air flow passage,
said bladder being adapted to expand against said duct when
pressurized and to retract from said duct when depressurized;
pneumatic power means coupled to said bladder for inflating said
bladder with pressurized air to cause it to expand against said
duct and seal the air flow passage in an isolation mode of
operation, and for pumping air from said bladder until its interior
pressure is reduced to a predetermined vacuum pressure level less
than ambient atmospheric pressure to cause it to assume a minimum
profile, collapsed condition and open the air flow passage in a
supply mode of operation;
an actuator coupled to said pneumatic power means for selectively
rendering said pneumatic power means operable in said isolation
mode and in said supply mode of operation; and,
power switching means coupled to said pneumatic power means
enabling operation of said pneumatic power means in response to the
interior air pressure of said air bladder being less than a first
pressure level corresponding with the inflation pressure of said
bladder when it is in the expanded, duct engaging condition, and
for inhibiting operation of said pumping means (a) in response to
the inflation pressure of said bladder being greater than said
first pressure level, or (b) in response to the collapsed pressure
of said bladder being less than a second pressure level below
ambient atmospheric pressure corresponding with the vacuum pressure
of said bladder when it is in the collapsed, minimum profile
condition.
3. Apparatus for opening and closing the air flow passage of an air
flow duct comprising, in combination:
an inflatable air bladder for insertion into the air flow duct,
said bladder being adapted to engage the air flow duct and close
the air flow passage when expanded, and to assume a minimum profile
condition and open the air flow passage when collapsed and
evacuated;
an air pump having inlet and discharge ports;
valve means for selectively coupling said bladder in fluid
communication with said pump in a bladder pressurizing mode and in
fluid communication with ambient atmosphere in a bladder evacuation
mode, said valve means having a first port coupled to ambient
atmosphere, a second port coupled to the pump discharge port, a
third port coupled to the pump inlet port and a fourth port coupled
to said bladder, the first valve port being connected in fluid
communication with the third valve port and the second valve port
being connected in fluid communication with the fourth valve port
in the bladder pressurizing mode, and the first valve port being
connected in fluid communiction with the second valve port and the
third valve port being connected in fluid communication with the
fourth valve port in the bladder evacuation mode;
actuating means coupled to said valve means for selectively
rendering said valve means operable in the bladder pressurizing
mode and in the bladder evacuation mode; and,
pressure responsive power switching means coupled to said pump for
enabling operation of said air pump in response to the pump
discharge port pressure being less than a first pressure level
corresponding with the inflation pressure of said bladder when it
is in the expanded, duct closed condition, and for inhibiting
operation of said pump (a) in response to the pump discharge port
pressure being greater than said first pressure level, or (b) in
response to the pump inlet port pressure being less than a second
pressure level below ambient atmospheric pressure corresponding
with the vacuum pressure of said bladder when it is in the
collapsed, minimum profile duct open condition.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates generally to energy management, and in
particular to air flow control in a heating, ventilating and air
conditioning system (HVAC) by selective zone isolation.
2. Description of the Prior Art:
Because of the rapidly rising costs of energy, the incentives to
conserve are increasing, both for domestic users as well as
industrial users. For most domestic users, home air conditioning
and heating accounts for a substantial portion of the annual energy
expense. Although most dwellings are insulated, a large amount of
energy is expended by the air conditioning compressor to pump
radiant heat absorbed by the dwelling structure out of the air
conditioned living space to the outside ambient air. Likewise, a
great deal of energy is expended by the furnace to replace heat
energy which is lost through the walls and ceiling of the dwelling
structure.
For energy conservation reasons, it is common practice to reduce
the degree of cooling or heating during periods of minimum
activity, for example at night, according to comfort requirements.
For example, the ambient temperature in a home can be reduced at
night while the occupants are asleep without causing any
discomfort. Additionally, the temperature can be reduced
substantially during the day when the dwelling is not occupied.
Such reduction in the nighttime temperature of the dwelling is
referred to as a "set-back" which results in a significant
reduction in fuel consumption for heating and cooling the
dwelling.
Although the night set-back thermostat provides energy savings, the
air conditioning compressor or furnace is still subjected to the
entire heat gain/loss loading of the dwelling, limited only by
upward or downward (depending on the season) temperature drift
through the entire home. Obvious comfort requirements restrict this
drift and limits savings potential in many cases.
It has been common practice by homeowners to reduce energy costs by
closing off certain rooms which are no longer in use. This is
commonly carried out by closing the outlet vent of the supply duct
for the room which is to be isolated. It will be appreciated that
while this may be an acceptable method on a long term basis, it
cannot be conveniently practiced on a daily basis. The requirement
to manually close and open the vent is subject to human failure and
neglect whereby cost savings are lost. Moreover, manual alteration
of the vent opening is not entirely satisfactory since the isolated
room will be uncomfortably cool or warm in the morning before its
vent manually opened and, due to the lag time of typical heating
and cooling systems, half an hour or more is usually required for
room temperature to reach a comfortable level for normal daytime
activities. Finally, most supply vents are located on the ceiling
at an elevation which cannot be conveniently reached without the
aid of a stepladder.
In some commercial installations, the flow of conditioned air
through an air supply duct is regulated by a moveable damper plate.
The position of the damper plate is established by a reversible
drive motor as a function of air velocity through the supply duct
and temperature of the air in the space being serviced. The
mechanical damper assembly is not well suited for retrofit
applications because of the extensive duct modification required
and the expense of the damper motor and damper control. Moreover,
the mechanical damper assembly is not suited for retrofit
installations in some cases because of the lack of adequate working
space around the supply ducts. Finally, the mechanical damper plate
must have clearance along its edges to allow it to rotate within
the damper. Thus, it cannot completely close off the air flow
passage. In such installations, the mechanical damper plate
modulates the conditioned air flow to accomodate temperature
changes in the air space being serviced, rather than completely
closing it off.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to
conserve energy by selectively isolating an activity zone of a
dwelling during periods of inactivity.
A related object of the invention is to provide selective zone
isolation for an HVAC system which is suited for retrofit
installation.
Another object of the invention is to provide an energy management
system for dwellings which automatically opens and closes selected
supply air ducts according to a preprogramed zone isolation and
service schedule.
Yet another object of the invention is to provide apparatus for
selectively sealing and opening a air duct which requires no
structural modification of the air duct.
SUMMARY OF THE INVENTION
The activity zone of a house, including the living room, dining
room, kitchen and game room are selectively isolated with respect
to the sleeping zone of the dwelling during nighttime intervals by
blocking the flow of conditioned air into the activity zone, while
allowing the normal flow of conditioned air into the sleeping zone.
Zone isolation is accomplished by blocking the air flow passage of
HVAC air flow ducts which supply conditioned air to the activity
zone. The air flow passage in each supply duct is selectively
blocked by an inflatable air bladder which is inserted into the air
flow passage. An air compressor is coupled to the bladder for
inflating it to cause it to expand against the sidewall of the duct
and seal the air flow passage during the isolation mode of
operation, and for pumping air from the bladder to cause it to
collapse and open the air flow passage during a conditioned air
supply mode of operation.
In the preferred embodiment, operation of the compressor is
coordinated by a solenoid controlled, four-way valve which ports
pressurized air to the air bladders during the zone isolation mode,
and directs the withdrawal of air from the air bladders during the
conditioned air supply interval. Operating power for the compressor
is provided by a pressure responsive power switch which applies
operating power to the compressor in response to compressor exhaust
port pressure being less than the pressure level corresponding with
a fully inflated air bladder (duct closed), and which removes
operating power from the compressor in response to the compressor
inlet port pressure being less than the pressure level
corresponding with the air bladder being in the collapsed condition
(duct open). Power to the compressor is interrupted when the
compressor exhaust port pressure exceeds the pressure level
required to fully inflate the bladders, or when the compressor
inlet port pressure drops below the pressure level required for
complete collapse of the bladders.
Supply duct isolation is provided by an inflatable bladder which is
adapted to be inserted into the air flow space of the duct. In the
isolation mode of operation, the air bladder is inflated with
pressurized air and expands against the inside sidewall surface of
the air flow duct, thereby closing the air flow passage and
blocking the flow of conditioned air. In the service mode of
operation, air is pumped out of the bladder until it is completely
collapsed, thereby opening the air flow passage of the supply duct
and permitting the flow of conditioned air through the duct.
The bladder is inflated and deflated by the electrically driven
compressor in cooperation with the four-way shuttle valve and a
timer. The timer is preprogramed to actuate the shuttle valve
during a zone isolation interval. During the isolation interval,
the four-way valve connects the suction line of the compressor to
draw ambient air and the high pressure exhaust port of the
compressor to pressurize the air bladder. During a service
interval, the timer actuation signal is removed, thereby allowing
the four-way shuttle valve to shift and connect the input port of
compressor to draw air from the pressurized bladders, while
exhausting the air into the surrounding environment.
The air bladders are installed merely by inserting them into the
supply air ducts which are to be selectively isolated. For retrofit
applications, the only modification required is to cut a small
access door and supply conduit feed-through opening in the main
supply plenum housing. The air bladders are manually inserted
through the access opening and into the designated supply ducts,
and the air supply conduit is routed through the feed-through
opening to the four-way valve.
The novel features which characterize the invention are set forth
in the apended claims. The nature of the invention, however, as
well as its essential features and advantages, will be more fully
comprehended upon consideration of an illustrative embodiment, when
read in conjunction with the accompaning drawings, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic diagram of a selective zone
isolation system as installed in a dwelling;
FIG. 2A is a perspective view of a supply air duct having an air
bladder pressurized to its fully expanded, duct closed
condition;
FIG. 2B is a view similar to FIG. 2A in which the air bladder is
collapsed in its duct open condition;
FIG. 3 is a perspective view of an air distribution plenum
illustrating a typical installation of air bladders in supply
conduits; and,
FIG. 4 is a simplified electrical and pneumatic diagram of the
selective zone isolation system shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the description which follows, like parts are marked throughout
the specification and drawings with the same reference numerals,
respectively. The figures are not necessarily drawn to scale and in
some instances proportions have been exaggerated in order to more
clearly depict certain features of the invention.
Refering now to FIG. 1, a selective zone isolation 10 is installed
in a family dwelling 12. The family dwelling 12 includes an
activity zone 14 and a sleeping zone 16. The activity zone
comprises a living room (LR), a game room (GR), kitchen (KIT) and a
dining room (DR), rooms which are utilized during the waking hours,
typically 7 A.M.-10 P.M. The sleeping zone 16 comprises a master
bedroom (MBR) and bedrooms (BR 1, BR 2). These rooms are utilized
as sleeping areas, typically from 10 P.M. to 7 A.M.
The rooms of the activity zone 14 are ventilated and conditioned
for comfort by a central heating and air conditioning system 18.
The central HVAC system includes a furnace (not illustrated) and
air cooling equipment, for example a compressor, condenser and
evaporator (not illustrated). Conditioned air produced by the
central HVAC unit 18 is circulated into the various rooms of the
dwelling through supply ducts 22, 24, 26, 28, 30, and 32. Each
supply duct has an inlet port connected to receive pressurized air
from a distribution plenum 34 and has an outlet port for
discharging the conditioned air into a living space through a
mechanical vent. The inlet ports are designated 20A, 22A, 24A, 26A,
28A, 30A, 32A and the mechanical vents are designated 20B, 22B,
24B, 26B, 28B, 30B, 32B, respectively.
The distribution plenum 34 is charged with conditioned air 36 which
is forced across a heat exchanger by a blower fan. During operation
of the HVAC system, the conditioned air 36 is circulated
intermittently through the supply ducts into the various rooms of
the dwelling and is returned to the inlet port of the heat
exchanger through return ducts (not illustrated).
According to an important aspect of the invention, energy is
conserved by selectively interrupting the flow of conditioned air
into the activity zone 14 during periods of inactivity, for example
at nighttime, while permitting the flow of conditioned air into the
sleeping zone 16. Zone isolation is accomplished by blocking each
supply duct 20, 22, 24 and 26 with an inflatable air bladder 38.
Referring to FIGS. 2A, 2B as typical installations, the air bladder
38 is inserted into the air flow passage 22C of conduit 22. The air
bladder 38 is pressurized and deflated through an air conduit 40.
In FIG. 2A, the air bladder is fully expanded against interior
sidewall surface 22D of the supply duct 22. The air bladder 38 is
constructed of an elastic material which permits it to conform with
the geometry of the interior sidewall surface 22D. As the bladder
38 expands, it is driven into engagement with the interior sidewall
22D, thereby sealing the air flow passage 22C. In this fully
inflated condition, the air bladder 38 blocks the flow of
conditioned air 36 through the flow passage 22C, thus isolating the
room (KIT) serviced by duct 22.
In FIG. 2B, the air bladder 38 is in its completely collapsed
condition which is produced by drawing the air from the bladder 38
through conduit 40 until the air pressure within the bladder 38 is
substantially below atmospheric pressure. In this duct open,
collapsed bladder condition, conditioned air 36 is circulated
freely through the flow passage 22C into the room being serviced
during a preprogramed conditioned air service interval.
Referring now to FIGS. 1 and 4, each bladder 38 is inflated and
deflated by an electrically driven compressor assembly 42 in
cooperation with a four-way shuttle valve 44 and a multiple channel
timer 46. The four-way shuttle valve 44 is mechanically shifted by
an electrical solenoid 48. The four-way valve 44 is capable of
operating in two modes, as schematically indicated in FIG. 4. As
illustrated in FIG. 4, timer 46 energizes solenoid 48 during a zone
isolation interval, with the four-way valve connecting the suction
line 50 to draw ambient air 52 and with the high pressure exhaust
line 54 connected to pressurize air supply conduit 40. During a
conditioned air service interval, the timer de-energizes the
solenoid 48, thereby allowing the four-way shuttle valve to shift
and connect the suction line 50 to draw air from the bladders 38
through conduit 40, while exhausting the air 56 into the
surrounding environment as it is pumped out of the bladders 38.
The timer 46 applies 110 VAC operating power to the solenoid 48
through conductors 58, 60 during the zone isolation interval. The
operating power is derived from the 110 VAC supply. Other operating
voltage levels, for example, 24 VAC, may be used to good advantage,
according to the specific power requirements of the operating
equipment and selected components.
Operating power for the compressor assembly 42 is also provided by
the 110 VAC household supply. The compressor assembly 42 includes a
pneumatic compressor P and an electrical drive motor M. The
compressor P has an inlet port 62 to which the suction line 50 is
connected, and an outlet port 64 to which the high pressure exhaust
line 54 is connected. The electrical motor M receives its operating
power from the 110 VAC household supply, through a pressure
presponsive electrical switch 66. The electrical motor M is
connected to the household supply through power conductor 68, 70
with the pressure responsive electrical switch 66 being connected
in series with the motor M. Compressor operating power is
selectively interrupted by the pressure responsive switch 66 in
response to certain compressor exhaust port and compressor inlet
port pressure conditions.
The pressure responsive power switch 66 has pressure sensing lines
72, 74 which are coupled to the compressor inlet port 62 and
compressor exhaust port 64, respectively. The pressure responsive
switch 66 is normally closed and opens only under high pressure or
low pressure operating conditions. That is, when the pressure at
the inlet port 62 of the compressor drops below the pressure level
corresponding with the air bladders 38 being in the collapsed (duct
open) condition, power to the compressor is interrupted.
Additionally, when the discharge port pressure exceeds the pressure
level required to fully inflate the bladders and close off the
supply ducts, the switch 66 opens, thereby interrupting electrical
power to the motor M.
The pressure responsive power switch 66 is closed and applies
operating power to the compressor compressor P in response to the
compressor exhaust port pressure being less than the pressure level
corresponding with the air bladders 38 being in the fully inflated
and expanded condition as illustrated in FIG. 3, during a zone
isolation interval. Operating power is also enabled to the
compressor through the pressure responsive switch in response to
the compressor compressor inlet port pressure being less than the
pressure level corresponding with the air bladders 38 being in a
collapsed, fully deflated condition as illustrated in FIG. 2B. Thus
the compressor compressor assembly 42 is cycled on and off
automatically to maintain the bladders 38 in the fully inflated
condition, or in the collapsed condition. The compressor assembly
42 is automatically interrupted in response to an over pressure
condition or an under pressure condition in the supply conduit
40.
The isolation zone 14 is protected against damaging temperature
excursions by a high-low limit thermostat switch 82 and a solenoid
controlled, single pole, single throw contactor 84. The contactor
84 is a single pole, single throw normally closed switch which is
opened by a solenoid 86. The thermostat 82 is normally opened and
closes in response to ambient temperature above or below a critical
temperature level. For example, during the heating mode of
operation, the theromstat 82 may be set to close for temperatures
below 40.degree. F. When the HVAC system is operated in the cooling
mode, the threshold level may be set for 90.degree. F. The high-low
thermostat 82 is connected in series electrical relation with the
solenoid 86 and is, therefore, capable of conducting line current
through its contacts. Power conductors 88, 90 couple the thermostat
to the solenoid 86 and a source of operating power (not
illustrated). When the temperature sensed by thermostat 82 reaches
a predetermined extreme value, for example less than 40.degree. F.,
it closes the series electrical circuit with the solenoid 86,
thereby actuating the normally closed contactor 84, and
interrupting the supply of operating power to solenoid 48. When
solenoid 48 is de-energized, the shuttle valve 44 shifts and
connects the inlet and exhaust conduits 50, 54 to draw air 56 from
the bladders 38 and discharge it into the surrounding environment.
When the bladders 38 have been completely deflated, the air
passages through each supply duct are opened, thereby allowing the
circulation of conditioned air. After the ambient temperature of
zone 14 rises to a safe temperature level, thermostat 82 opens,
thereby allowing the bladders 38 to reinflate and return zone 14 to
the isolated condition. High temperature limit operation occurs in
the same manner.
Referring again to FIG. 3, an access door is cut into the top of
the plenum 34 and is sealed by a removeable cover door 76. In a
retrofit installation, the door 76 is removed, thereby providing
access to the plenum chamber 78 and the inlet ports 20A, 22A, 24A,
and 26A. The air bladders 38 are installed in their completely
collapsed condition by inserting them through the access door
opening and into the flow passages of the selected supply ducts 20,
22, 24, and 26. The inflatable bladders 38 are separately coupled
to the supply conduit 40 by conduit coupling sections 40A, 40B, 40C
and 40D, respectively. The supply conduit 40 is routed through a
small feed-through opening 80 formed in the plenum housing 34. The
feed-through opening 80 is sealed after installation is
completed.
The timer 46 can be located at any convenient wall location, for
example adjacent the system thermostat, and the compressor, shuttle
valve and pressure switch can be located in the attic.
In the preferred embodiment, separate system thermostats 92, 94 are
mounted in the activity zone 14 and the sleeping zone 16,
respectively. The system thermostat 92 controls the operation of
the HVAC unit 18 during daylight hours, typically 7 A.M.-10 P.M.
The thermostat 94 located in the sleeping zone 16 controls the HVAC
unit 18 during nighttime hours, typically 10 P.M.-7 A.M. Control
conductors 96 leading from system thermostat 92 and control
conductors 98 leading from system thermostat 94 are selectively
coupled to HVAC control circuit 100 by a solenoid actuated four
pole, double throw relay 102. The relay 102 is actuated by an
electrical solenoid 104 in response to actuating current conducted
by the multi-channel timer 46 through power conductors 106, 108. At
a preselected time, for example 6 A.M., the multi-channel timer 46
conducts actuating current to solenoid 104, thereby causing relay
102 to switch its output control conductors 110 from the nighttime
system thermostat 94 to the daytime system thermostat 92. Then, at
10:30 P.M., when the programed interval in timer 46 has elapsed,
the solenoid 104 is de-energized, thereby turning control of HVAC
unit 18 to the nighttime thermostat 94.
It is desirable to exercise control of the HVAC unit 18 with dual
system thermostats so that the isolation zone will quickly return
to a comfortable temperature, at least by the time that daytime
activities begin. Additionally, during the heating season, the
occupants of the dwelling would welcome an additional flow of warm
air brought about by switching the system control to the activity
zone thermostat. This will cause a momentary rise in temperature in
the conditioned sleeping zone 16. However, during the cooling
season, an additional flow of conditioned cool air would not be as
welcome during the early morning hours since body temperature drops
during sleep. Therefore, during the cooling season, the timer 46 is
programed to switch system control to the activity zone thermostat
92 to coincide with the end of the sleeping period.
Although a preferred embodiment of the invention has been described
in detail, it should be understood that various changes,
substitutions and alterations can be made therein without departing
from the spirit and scope of the invention as defined by the
appended claims.
* * * * *